1. Field of the Invention
The present invention generally relates to a coordinate-detecting device used as input means for personal computers and word processors and a coordinate input pad thereof, and particularly relates to a coordinate-detecting device of a voltage-detecting type which generates coordinate data based on voltage values detected when there is a touch on a coordinate input panel having an x-coordinate and a Y-coordinate, and the coordinate input pad thereof.
2. Description of the Related Art
Recently, information-processing devices such as personal computers and word processors are provided with improved operation systems and other improved characteristics so as to be easily manipulated by the users. Also, for such information processing devices, coordinate-detecting devices are commonly used as pointing devices rather than mouses. This is because the coordinate-detecting devices are simple to use.
The coordinate-detecting device may be of an electromagnetic induction type, a capacitive coupling type or a resistive film type. Among those types of devices, the resistive film type is often used because of its various advantages such as a simple structure, a reduced cost and a reduced thickness.
In the following, a coordinate-detecting device of the prior art will be described with reference to FIG. 3.
FIG. 3 shows a coordinate-detecting device of the prior art including a coordinate input pad 201 and a detecting part 202. The coordinate input pad 201 serves as an operating surface via which a user can input information into an information-processing device such as a personal computer or a word processor. The detecting part 202 applies a voltage to the coordinate input pad 201 and then detects a position of a contact point on the coordinate input pad 201. Thus, the coordinate-detecting device outputs switching data and coordinate data when there is a touch on the coordinate input pad 201.
FIG. 1A is a perspective diagram showing a coordinate input pad used in the coordinate-detecting device of the related art. The coordinate input pad has two resistive films 203, 204 opposing each other with a plurality of dot spacers 216 placed between the resistivefilms 203, 204. The resistive films 203, 204 are provided with pairs of electrodes 205, 206 and 207, 208, respectively, which are formed along the edges and located at opposite sides of central input regions 215.
The resistivefilms 203, 204 are located such that the pair of electrodes 205, 206 and the pair of electrodes 207, 208 formed on the respective resistive films are perpendicular to each other. For example, as shown in FIG. 3, the electrode 205 parallel to the x-axis may be used for detecting a voltage corresponding to a y-coordinate. Also, the electrode 207 parallel to the y-axis may be used for detecting a voltage corresponding to an x-coordinate. It is to be noted that the plurality of dot spacers 216 made of an insulating material is provided in order to prevent any short-circuit between the two resistive films 203, 204 during a normal state.
The detecting part 202 includes a pair of transistors 209, 210 for applying a voltage across the pair of electrodes 205, 206 on the resistive film 203 and a pair of transistors 211, 212 for applying a voltage across the pair of electrodes 207, 208 on the resistive film 204. The detecting part 202 applies voltages to the resistive films 203, 204 by alternately turning on the pair of transistors 209, 210 and the pair of transistors 211, 212.
Further, the detecting part 202 includes a control part 213 for controlling the transistors 209, 210, 211, 212 and a voltage-detecting part 214 for detecting a voltage corresponding to a pressed-down point on the coordinate input pad 201. Thus, the detecting part 202 detects a coordinate of the pressed-down point on the coordinate input pad 201.
With the coordinate-detecting device of the above structure, when a point on the coordinate input pad 201 is pressed down, the two resistive films 203, 204 will be in contact at the pressed-down point. If a voltage has been applied across the electrodes 205, 206, the voltage will be divided at the contact point and a voltage representing the y-coordinate will be output via the electrode 207. Also, if a voltage has been applied across the electrodes 207, 208, the voltage will be divided at the contact point and a voltage representing the x-coordinate will be output via the electrode 205.
After detecting the voltages representing the x-coordinate and the y-coordinate, the voltage-detecting part 214 sends the voltages to the control part 213. At the control part 213, coordinate data or switching data of the contact point will be generated based on the voltages. Finally, the generated data is output from the control part 213.
The coordinate-detecting device of the prior art is advantageous in that, when the resistive films 203, 204 are flexed due to a factor such as a thermal stress, the opposing resistive films 203, 204 are prevented from coming into contact by means of the dot spacers 216 provided at appropriate intervals. Therefore, the resistive films 203, 204 will be in contact only when there is a touch on the coordinate input pad 201.
FIGS. 2A and 2B are cross-sectional diagrams showing problematic aspects of the coordinate input pad of the related art. As shown in FIG. 2A, the coordinate-detecting device of the prior art is provided with dot spacers made of an insulating material between opposing resistive films. Therefore, when there is a touch on the coordinate input pad at a point directly or substantially above a particular dot spacer, the resistive films will be in contact at locations surrounding the dot spacer (see FIG. 2B). Thus, detected data may be unstable.
In order to avoid such a problem and thus improve operability, it is necessary to increase intervals between the dot spacers while reducing the size and height of the dot spacers.
However, when the configuration of the dot spacers is altered as described above, there is a greater possibility that the resistive films are short-circuited since a gap between the resistive films may be narrowed due to a distortion or bowing of the resistive films.
Also, with the coordinate-detecting device of the prior art, the resistive films are joined by means of an adhesive layer of an order of several tens of micrometers. With this structure, there may be joint gaps at the joining part because of a level difference due to patterns provided at the joining part or because of the roughness of the surface of a resist layer. With such joint gaps, when the coordinate input pad is pressed over a comparatively large area, some of the air existing between the resistive films will escape via the joint gaps. Once the air has escaped, not enough air will immediately flow back to the space between the resistive films even if the pressure on the coordinate input pad is released. Therefore, the coordinate-detecting device of the prior art has a disadvantage that the resistive films may remain in contact for a considerable time.
Accordingly, it is a general object of the present invention to provide a coordinate-detecting device and a coordinate input pad used in the coordinate-detecting device which can solve the above problems.
It is another and more specific object of the present invention to provide a coordinate-detecting device which can detect accurate coordinate data at any point on an operating surface of a coordinate input pad.
In order to achieve the above objects according to the present invention, a coordinate-detecting device of a voltage-detecting type includes a coordinate input pad having an upper sheet and a lower sheet opposing each other at a predetermined gap by a repulsive force between magnetic poles with the same polarity.
The coordinate-detecting device described above does not include dot spacers. Therefore, the resistive films may be in contact at any locations on the operating surface, whereas in the related art, the resistive films may be in contact at location surrounding a dot spacer and thus detected data may be unstable.
It is still another object of the present invention to provide a coordinate-detecting device which can withstand a deformation such as a distortion due to deterioration with age of the upper sheet.
In order to achieve the above object according to the present invention, the upper sheet and the lower sheet oppose each other at a predetermined gap by a tension in the upper sheet.
Also, in order to achieve the above object according to the present invention, the upper sheet and the lower sheet oppose each other at a predetermined gap by a central part of the upper sheet being bent upwards.
Further, in order to achieve the above object according to the present invention, the upper sheet and the lower sheet oppose each other at a predetermined gap by a central part of the lower sheet being bent downwards.
With any one of the coordinate-detecting devices described above, it is possible to prevent problems related to an unintended short circuit.
It is yet another object of the present invention to provide a coordinate-detecting device which can prevent the upper and lower sheets from remaining in contact for a considerable time.
In order to achieve the above object according to the present invention, a cavity is formed between the upper sheet and the lower sheet opposing each other at a predetermined gap, and the lower sheet is provided on a mounting board, communicating holes being provided through the lower sheet and the mounting board for establishing a communication between the cavity and external air, the communication being established depending on a state of pressure on the coordinate input pad.
Also, in order to achieve the above object according to the present invention, the upper sheet and the lower sheet oppose each other at a predetermined gap by the upper and lower sheets being joined together via a frame-like adhesive film of a thick-film type, a sealed cavity being formed between the upper and lower sheets.
With either one of the coordinate-detecting devices described above, it is possible to obtain accurate coordinate data.
In the present invention, coordinate input pads used in the above-described coordinate-detecting devices are also disclosed.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.